Glass substitute and process of preparing



fi ld? If V Patented Mar. 12, 1940 z eamz GLASS SUBSTITUTE AND PROCESS OF PREPARING I Otto Rihm and walter Bauer, Darmstadt, Gery, assignors to Biihm No Drawing. Application July 2, 1934, Serial No. f

733,518. In Germany October 26, 1928 [I 5 2 Claims.

& Haas Company,

This invention relates to the manufacture of then treated as above for the preparation of glass substitutes from polymerizable unsaturated organic compounds, particularly the derivatives of methacrylic acid alone or in mixture of each 5 other with other polymerizable substances.

These substances can be polymerized by the action of light, heat and/or of catalysts such as organic and inorganic peroxides, oxygen, etc., to yield colorless, transparent materials which are eminently suited for use as substitutes for glass in many of its applications. The polymerized material may be manufactured in any desired form so that it may be substituted for glass in windows, automobile Windshields, lenses for optical instruments,'eyeglasses, goggles etc. On account of its low specific gravity as compared with ordinary glass, it is very suitable for making window lights for aircraft.

lt has been found that the polymerized esters 9L acrylic a ry lp. ci s. va y. con aPlvln h r nera aspaals e merel n i e riz ation products of theesters of methacrylic acid are harder than those of the corresponding esters of acrylic aci d and the hardness in both 95 series decreases as the number of carbon atoms in the alcohol radical of the ester is increased. F; -Thus p olymerized methyl methacrylate is th e haFiest of' all t l 'iese ma t erlals and consequently is best suited as as ubs titute for glassior those 3 'd; -Whe're the greatest haIdnssis'nBt necessary, the i polymerized methyl methacrylate may be modified by the addition of suitable plasticizers or other polymerized products such as the esters of 5 acrylic acid or the higher esters of methacrylic,

acid. When more than one ester of acrylic or methacrylic acid is used, they may be mixed- 4 a after polymerization but preferably the monomeric substances are mixed and then subjected "5 jointly to polymerizing influences. The materials obtained in this way are superior to those obtained by mixing the polymerized materials.

For making. sheets of this material for use as 45 window glass substitutes, it may be first dissolved in a suitable solvent and then poured out in a large flat container and the solvent evaporated. After the evaporation of the solvent,

the sheet may be ground and polished if neces- 50 sary and cut to any desired size. For making lenses for goggles, etc., a thin sheet may be prepared as above and the lenses out from this sheet. If the use of a solvent is objectionable for any reason, the molten material may be so poured on a hot surface and allowed to cool and o purposes where hardness is the prime requisite.

' window lights or lenses. Especially clear glass substitutes are obtained when the monomeric or the partialhr polymerized substances are polymerized at as low a temperature as is practical andwith the use of only very small amounts of catalyst.

Lenses for optical purposes may be made in several ways such for instance, as cutting slugs from sheets of the material and then either grinding them and polishing directly or the slug may be placed in a mold of suitable dimensions and heated under pressure until it attains the shape of the mold. After removal from the mold. it may be ground and polished if necessary.

' Lenses may also be made by placing powdered polymerized material of this type in a mold and forming it under the action of heat and pressure. Slugs of suitable size for molding may also be made by extruding the polymerized material through a die and cutting the rod so made to the proper length for use in the mold.

This material has many advantages 9 ver ordinary glass. It is considerably more transparent 'tfiltffiidlet light. It is not'brittle and there-" fore cannot be so easily broken by shock or blow.

It will not crack when exposed to sudden and uneven changes of temperature. Its index gi refraction varies according to the nature of the .ii i esn qieggana this may b irliifitlsd to s'uit'any p rposes by the addition Fi'ia'thermaterialsghaving a difierent index 0t 7551mm? 7 ausep s m ptle es J E 3 f may be built up which can be corrected forboth l spherical and chromatic aberration, in a manj ner similar to that prevalent in the fabrication of glass lenses. 7

In order to illustrate the invention, the following examples are given but it is understood these do not limit the .inventlon in any way to the specific materials or mixtures given, since the invention may be otherwise practiced within the scope of the appended claims:

Example 1.Monomeric ethyl methacrylate or partially polymerized ethyl methacrylate is heated to about 70 C. until polymerization is complete. If desired a small amount of catalyst such as benzoyl peroxide, for instance 0.03% may be added to the monomeric substance before polymerization. The polymerization product thus obtained may be used as a substitute for window glass, lenses for spectacles, goggles, etc.

Example 2.A mixture of 60 parts of methyl methacrylate and 40 parts of ethyl acrylate is polymerized as "in Example 1. The sheet thus obtained may be used in the same way as the product of Example 1, but the material is somewhat softer.

Example 3.A lens suitable for optical work may be molded as follows:

Methyl-methacrylate is polymerized and reduced to a powder in any desired manner. This powder is then placed in a mold of suitable dimensions and pressed under a pressure of about 1000 pounds per square inch at a temperature of about 120 to 130 C. After cooling the finished article may be removed from the mold and if necessary may be ground and polished to the where a flexible transparent material is desired,

or to change the optical properties in the case of lenses, other substances may be mixed with the polymer before, during or after polymerization. Softening materials which may be used are the esters of phthalic acid, tartaric acid, phosphoric acid, etc., all of which will change both physical and optical properties of the polymerized material.

fiefft of paraifln oil, 3 mm. thick, will transmit liriits, whereas ordinary glass of equal thickness will not transmit light having a wave length less thifiboiit 2970 Angstrom units. A mercury vapor lairipwa's the source of light employed in making these measurements. The above mixture of polymethyl methacrylate and paraili'n oil had a refractive index of 1.485.

e especlallymheiik ud .o jzhe.slasssubs i:

' tute so a sithe poly-methyl-methacrylate may be E1bfil te..

We claim: 1. A lens for correcting defective vision comprising a polymerized lower alkyl ester of methacrylic acid.

2. A lens for correcting defective vision'consisting essentially of polymerized methyl methacrylate.

used also forjcoating of softer qualities of glass orro RCSHM. WALTER. BAUER.

light having a wave length of 2750 Angstrom 

